The complement system is activated via three distinct pathways; the classical pathway, the lectin pathway and the alternative complement pathway (AP). The classical pathway is activated via antigen-antibody complexes. The lectin pathway is a variation of the classical pathway and the alternative pathway is activated by foreign material, artificial surfaces, dead tissues, bacteria, dead yeast cells.
Activation of the classical pathway generates C3a, C4a, C5a and C5b-9 molecules which activates a variety of cells in response to host defense. In pathological conditions, as a result of activation of the alternative pathway, anaphylatoxins C3a, C5a are formed which activate cells and C5b-9 molecules also known as the membrane attack complex (MAC) that damage tissues. Collectively these molecules mediate inflammation via cellular activation and release of inflammatory mediators. In addition to the role of C5b-9 as a lytic pore-forming complex, there is strong evidence that the depositing of sublytic MAC may play an important role in inflammation.
The classical complement pathway is important for host defense against pathogens. The alternative complement pathway is activated in pathological inflammation. Elevated levels of C3a, C5a, and C5b-9 have been found associated with multiple acute and chronic disease conditions. Therefore, inhibition of disease-induced AP activation is important for clinical benefit in the diseases where complement activation plays a role in disease pathology.
In addition to its essential role in immune defense, the complement system contributes to tissue damage in many clinical conditions. The activities included in the complement biochemical cascade present a potential threat to host tissue. An example includes the indiscriminate release of destructive enzymes possibly causing host cell lysis. Thus, there is a pressing need to develop therapeutically effective complement inhibitors to prevent these adverse effects.
In a disease condition where AP activation contributes to disease pathology, elevated levels of C3a, C5a and C5b-9 molecules are found in serum, plasma, blood or other body fluids representative of the disease. Production and inhibition of each of these molecules via different mechanisms is important for diseases. One possible mechanism for inhibiting the formation of the PC3bBb complex is via the use of an anti-Bb antibody. Thus blocking/inhibiting or preventing AP activation via depleting Bb, neutralizing Bb, or inactivating Bb remains an important therapeutic strategy.
The present invention relates to developed humanized and chimeric antibody sequences that are novel and provide targeted binding to factor Bb. The binding of such humanized/chimeric antibodies to factor Bb prevents activity of convertase. Such antibodies also prevent conversion of PC3bB into PC3bBb via binding the factor D cleavage site on factor B of the PC3bB complex. These antibodies do not inhibit properdin binding to C3b. Anti-factor Bb agents that bind Bb and prevent PC3bBb activity and prevent formation of new C3 convertase include, but are not limited to, monoclonal and polyclonal antibodies, chimeric, humanized, fully human, and nano-antibodies, Full length and fragments thereof, including IgG, Fab, Fab′, F(ab′)2, and IgGs. The antibodies of the present invention inhibit the formation of C3a, C5a, and C5b-9 which drive inflammation and also amplify the AP activation process.
Aptamers, small molecules, and SiRNA can also neutralize Bb binding to the PC3bB complex and prevent production of AP induced production of C3a, C5a, and C5b-9. As a result, cellular activation, inflammation and release of inflammatory mediators are also prevented. Because AP activation is linked to various acute and chronic human diseases, the blockade with anti-Bb agents will also block the inflammation process providing clinical benefit to mammals treated with the anti-Bb monoclonal antibodies.
Complement is one of several factors involved in pathogenesis and could be a significant pathological mechanism that offers an effective point for clinical control. The need for effective complement inhibitory drugs is signified by growing recognition of the importance of complement-mediated tissue injury in a variety of disease states. Despite this, currently there is a complete absence of approved drugs for human use that specifically target and inhibit complement activation.
Factor B plays a key role in the amplification loop of the alternative pathway since it provides the catalytic subunit, Bb, for C3-convertase (PC3bBb). Antibodies that inhibit C3b binding to Ba have been developed but none that inhibit the activity of the Bb. Factor B by itself is a zymogen with no known catalytic activity. After binding to PC3b complex, factor B is cleaved by factor D to release Ba. It has been shown that factor B binds C3b through regions found within each of the Ba and Bb subunits Inhibitors of factor Bb binders should results of selective inhibition of factor B function, thereby preventing formation of C3a, C5a and C5b-9, which are responsible for many deleterious effects.
Based on the results described in this patent application, we developed humanized and chimeric antibodies that bind the catalytic domain of factor B and prevent the activity of the PC3bBb, bind the factor D cleavage site on Bb and prevent the formation of additional PC3bBb molecules. These antibodies do not inhibit C3b binding to factor B as such binding events are shown to be mediated via Ba domain of factor B. This application developed humanized and chimeric anti-Bb specific inhibitors or inhibition methods that (a) will prevent factor B function by blocking PC3bBb activity and/or (b) suppress factor B cleavage that prevents Bb generation. These inhibitors appear to be inactivators of the C3 convertase enzymatic activity without disrupting the factor B interaction with C3b. We have evaluated the inhibitory activity of the anti-factor Bb antibodies for their potential role in blocking the AP activation. These antibodies prevent factor B function both in vitro and in whole blood. Other anti-factor Ba monoclonal antibodies have also been developed and tested in animal models of disease but not part of the current invention. These anti-Ba antibodies prevent factor B binding to C3b and hence block the activation of the complement cascade.
This invention is designed to inhibit the functional activity of Bb and its progressive effects in pathological conditions by use of an anti-Bb antibody.